The present invention relates to a method of automatically adjusting a speed controller to an elastomechanical controlled system.
Various filter options in the current setpoint channel of the speed controller are usually available for optimal adjustment of drive systems to an elastomechanical system such as a numerically controlled machine tool, a robot, etc. A good knowledge of automatic control engineering is required to optimally utilize these filter options.
In the past, setting the filter has routinely been left to the user. This requires knowledge of automatic control engineering to correctly evaluate frequency responses measured manually, and knowledge of the drive system in order to correctly interpret the available measurement functions.
In addition to a conventional manual adjustment of the above-mentioned filter options of the speed controller to the elastomechanical system, the behavior of the controlled system (stimulation of pulses or sudden changes) is recorded and optimized according to time functions with automatic setting of the speed controller in the time range. The natural frequencies of a multi-mass oscillator can be determined in the time range only with a great deal of inaccuracy and, thus, they can hardly be controlled. Therefore, specific filtering of the resonant frequency, which might be critical for the speed controller, is impossible with the conventional technique. Only inadequate adjustment of the controller can be performed by low-order filters (e.g., current setpoint or actual speed value PT1 filters).
An object of the present invention is to create a method of automatic adjustment of a speed controller to an elastomechanical controlled system which relieves the user of manual optimization activities while also permitting a better adjustment in comparison with the prior art.
According to the present invention, this object is achieved by providing a method which includes the following steps:
1.1 calculating a transfer function for the mechanical frequency response, in particular using a Fourier transform into the frequency range,
1.2 identifying pole positions and zero positions in the mechanical frequency response and storing the pole positions thus found in a buffer memory,
1.3 calculating a transfer function for the closed speed control circuit, in particular using a Fourier transform into the frequency range,
1.4 identifying pole positions and zero positions in the transfer function of the closed speed control circuit,
1.5 selecting the pole position with the largest amplitude from the pole positions of the closed speed control circuit and assigning a corresponding pole position in the mechanical frequency response,
1.6 setting filter parameters for the respective pole position in the mechanical frequency response according to the respective pole position frequency and zero position frequency for filtering the current setpoints,
1.7 repeating steps 1.4 through 1.6 until a sufficiently accurate adjustment of the speed controller has been achieved and no further filtering is necessary.
The present invention is thus based in principle on performing all the required measurements to identify the elastomechanical controlled system and simulation calculations on the-speed controller in the frequency range. This has the advantage that multi-mass oscillators can be identified unambiguously in the frequency range and thus can be controlled easily.
According to a first advantageous embodiment of the method according to the present invention, the mechanical frequency response can be determined especially effectively. This is accomplished with the following additional steps:
2.1 stimulating the elastomechanical system to oscillate, in particular by applying white noise to the current setpoint with the current control circuit closed,
2.2 measuring actual speed values and actual current values,
2.3 performing Fourier transform of the measured values into the frequency range.
In another advantageous embodiment of the method according to the present invention, an especially good frequency resolution over the entire measuring range is made possible by the following additional steps:
3.1 performing steps 2.2, 2.3 and 1.1 once in the possible frequency range of the speed controller, then another time at a quarter of this frequency,
3.2 combining the two measurements to a common transfer function.
According to another advantageous embodiment of the method according to the present invention, additional influences on the measurements at the upper and lower frequency limits are eliminated. This is accomplished by the following additional step:
4.1 analyzing only the middle frequency range of the transfer function for the mechanical frequency response after smoothing by averaging.
In another advantageous embodiment of the method according to the present invention, an especially advantageous determination of the transfer function of the closed speed control circuit is made possible by the following additional steps:
5.1 measuring actual current values and current setpoints with a closed speed control circuit, with white noise in particular being injected into the current setpoint,
5.2 performing Fourier transform of the measured values to the frequency range.
In another advantageous embodiment of the method according to the present invention, optimal control parameters for the gain and the reset time of the speed controller can be determined by the following additional steps:
6.1 repeating step 1.3 while increasing the gain of the speed controller until the amplitude of the transfer function exceeds the value of a stored characteristic curve of the desired dynamics at any point,
6.2 repeating step 1.3 while reducing the reset time of the speed controller until the amplitude of the transfer function exceeds the value of another stored characteristic curve at any point.